KR20180020928A - Anode Material Comprising Silicon flake and the Preparing Method of Silicon flake - Google Patents

Abstract

The present invention relates to: an anode material which is represented by chemical formula 1, xSi·(1-x)A, and includes silicon flakes having a hyperporous structure as an active material; and a manufacturing method of the silicon flakes. In the chemical formula 1, x satisfies 0.5 <= x <= 1.0 and A is impurity and is at least one compound selected from a group consisting of Al_2O_3, MgO, SiO_2, GeO_2, Fe_2O_3, CaO, TiO_2, Na_2O K_2O, CuO, ZnO, NiO, Zr_2O_3, Cr_2O_3, and BaO. The present invention can improve lifespan characteristics and rate characteristics.

Description

[0001] The present invention relates to an anode material including a silicon flake and a method for manufacturing the silicon flake,

The present invention relates to an anode material comprising a silicon flake and a process for producing the silicon flake.

Due to the rapid increase in the use of fossil fuels, the demand for the use of alternative energy and clean energy is increasing. As a part of this trend, the most active field of research is electric power generation and storage.

At present, a typical example of an electrochemical device utilizing such electrochemical energy is a secondary battery, and the use area thereof is gradually increasing.

2. Description of the Related Art [0002] Recently, as technology development and demand for portable devices such as portable computers, portable phones, and cameras have increased, the demand for secondary batteries as energy sources has increased sharply. Among such secondary batteries, they exhibit high energy density and operating potential, Many studies have been made on a lithium secondary battery having a long self discharge rate, and it has been commercialized and widely used.

In addition, as interest in environmental issues grows, research on electric vehicles and hybrid electric vehicles that can replace fossil-fueled vehicles such as gasoline vehicles and diesel vehicles, which are one of the major causes of air pollution, have. Although nickel-metal hydride secondary batteries are mainly used as power sources for such electric vehicles and hybrid electric vehicles, researches using lithium secondary batteries having high energy density and discharge voltage are being actively carried out, and they are in the commercialization stage.

As an anode active material of a lithium secondary battery, a material containing graphite is widely used. The average potential when the material containing graphite releases lithium is about 0.2 V (based on Li / Li +), and the potential thereof changes relatively smoothly during discharging. This has the advantage that the voltage of the battery is high and constant. However, since the electrical capacity per unit mass of the graphite material is as small as 372 mAh / g, the capacity of the graphite material at present is improved close to the theoretical capacity, so that the additional capacity increase is difficult.

In order to further increase the capacity of the lithium secondary battery, various anode active materials have been studied. As a high capacity negative electrode active material, a material which forms an intermetallic compound with lithium, for example, silicon or tin, is expected as a promising negative electrode active material. Especially, silicon is an alloy type anode active material having a theoretical capacity (4,200 mAh / g) higher than that of graphite by about 10 times or more, and has been attracting attention as an anode active material of lithium secondary batteries today.

However, since silicon has a large volume change (~ 300%) during charging and discharging, physical contact between the materials is broken and fragmentation occurs, the ionic conductivity and electric conductivity are rapidly reduced, see.

Accordingly, a bottom-up method of designing / synthesizing Si having a nanostructure capable of solving the problem caused by a change in the volume of Si has received great attention in recent years. However, since the manufacturing process is complicated, the yield is low, and the manufacturing cost is high, There is a drawback in that it is insufficient.

Therefore, in order to apply silicon to a lithium secondary battery, it is highly necessary to develop a technique for improving lifetime characteristics and rate characteristics and minimizing volume change during charging and discharging.

SUMMARY OF THE INVENTION Accordingly, the present invention has been made to solve the above-mentioned problems of the prior art and the technical problems required from the past.

The inventors of the present application have conducted intensive research and various experiments and have found that when synthesizing flake-shaped silicon of an initial hollow structure by using a metal reducing agent from cheap clay, the manufacturing cost is reduced and the manufacturing process is simplified In addition, it has been confirmed that when the lithium secondary battery is manufactured by using the formed silicon flake as the negative electrode active material, the volumetric expansion during charging and discharging is buffered, and the life characteristic and the rate characteristic are both improved. .

The anode material of the present invention for achieving this object is characterized by including a silicone flake represented by the following formula (1) and having an initial hyperporous structure as an active material.

xSi (1-x) A (One)

In this formula,

0.5? X? 1.0;

A is an _{impurity, Al 2 O 3, MgO,} SiO 2, GeO 2, Fe 2 O 3, CaO, TiO 2, Na 2 OK 2 O, CuO, ZnO, NiO, Zr 2 O 3, Cr 2 O 3 And BaO.

Here, x is a weight ratio, and specifically, the 'silicon flake' is a plate in which silicon atoms having a two-dimensional crystal form or a tetrahedral crystal form are two-dimensionally periodically arranged, Structure or a substantially plate-like structure.

In addition, the 'hyperporous structure' refers to a structure in which large pores, hollow pores, and micropores are formed together when classified based on the pore size.

Thus, the silicon flake having the initial hollow structure can be prepared, for example, as a large pore having a pore size in the range of more than 50 nm to 500 nm, a hollow electrode having a pore size of more than 2 nm to 50 nm, Lt; RTI ID = 0.0 &gt; 2 nm. &Lt; / RTI &gt;

Such an initial hollow structure is formed when the silicon flakes of the present invention are synthesized. As described below, the silicon flakes of the present invention are synthesized by a metal thermal reduction method in which clay and a metal reducing agent are heat-treated. In this case, through the surface reaction of the clay and the metal reducing agent, mesopores and micropores are formed together on the surface of the clay, and the large pores are not formed. Thereafter, as the reaction progresses, the metal reducing agent that has penetrated into the clay through the mesopores and micropores formed on the surface causes an internal reduction reaction, and the metal oxides formed therein form a pore later The post-treatment for removing the metal oxide forms an air gap in the place of the metal oxide, thereby completing the initial hollow structure.

In the case of using the silicon flakes having the initial open structure as the negative electrode active material, the expansion of the silicon volume at the time of charge and discharge can be mitigated by the initial hole structure, and the moving distance of the lithium ion is reduced while widening the contact area with the electrolyte It is possible to exhibit an effect of significantly improving lifetime characteristics and rate characteristics.

The average pore diameter of the pores of the silicon flakes having the initial pore structure for realizing the intended effect can be more effectively exhibited and the volume of the pore of the silicon flakes having the initial pore structure is 100 nm to 150 nm, % Porosity, in particular 10% to 30% porosity.

In addition, the BET surface area of the silicon flakes may be from 70 m ² / g to 250 m ² / g. In detail, it may be 120 m ² / g to 210 m ² / g, and more specifically 150 m ² / g to 190 m ² / g.

Here, the porosity was roughly calculated based on the total volume of pores and the tap density, and the BET surface area was measured by a nitrogen adsorption-desorption isotherm measurement using a Micromeritics ASAP 2020 instrument . In addition, the average pore diameter was calculated by applying the BJH (Barrett, Johner and Halenda) equation to the above results.

The silicone flakes may also have a thickness of 20 to 100 nm and may have a size of 200 nm to 50 탆, but are not limited thereto.

However, when the electrolyte membrane is formed to be thin and large enough to satisfy the above range, it is more preferable that the electrolyte membrane is easily impregnated while effectively reducing the moving distance of lithium ions. Specifically, the silicon flakes may have a thickness of 30 to 50 nm and may have a size of 1 to 5 占 퐉.

One such silicone flake may be formed when one unit (one unit) of the silicone flakes is formed in a stacked configuration. However, depending on the synthesis conditions for forming the silicon flakes, two to six silicon flakes, specifically, two to four silicon flakes Flakes may be stacked, but not limited thereto. When used as a negative electrode active material of a lithium secondary battery, two or more silicon flakes may be used in a laminated form. Accordingly, it is a matter of course that the 'including silicon flakes as an active material' includes a case where one or more silicon flakes are laminated when the silicon flakes are used as one unit.

On the other hand, when used as an active material, the silicon flakes according to the present invention can be carbon-coated to further improve the rate characteristics by increasing the electron conductivity.

At this time, the carbon coating can be carried out as an additional step in the process of manufacturing the silicon flake, and the concrete contents will be described in detail in the following production method.

The carbon coating may have a thickness of 1 to 100 nm, in particular 3 to 30 nm, more particularly 5 nm to 15 nm.

When the above range is satisfied, the rate characteristics to be obtained from the carbon coating are improved, the carbon coating can be uniformly formed, and as a result, the electrochemical performance is improved and the silicon content So that the problem of capacity reduction can be prevented.

On the other hand, the present invention also relates to a method for producing the silicone flake,

i) heat treating the mixture of clay and metal reducing agent at 500 to 800 degrees Celsius for 30 minutes to 6 hours;

ii) stirring the heat-treated mixture in an acidic solution; And

iii) obtaining an initial hollow structure silicon flake from the result of the stirring;

And a method for producing a silicon flake.

When a uniform mixture of the clay and the metal reducing agent is reacted in the vicinity of the melting point of the metal reducing agent as described above, the metal reducing agent begins to melt, causing a reduction reaction on the surface of the clay, And an excessive amount of heat is released while being reduced. The amount of heat released is transferred to the lower layer of the metal oxide in the clay, and the metal oxide plays a role of a negative catalyst, and plays a role of a heat scavenger that mitigates an excessive amount of calories generated from the reduction reaction do. Then, after the acidic solution post-treatment to remove the metal oxide, a large pore is formed in the place of the metal oxide to obtain silicon flakes having the original hollow structure together with the original hollow pores and micropores.

At this time, the clay used for obtaining the silicon flakes may have a layered structure, and in particular, a structure corresponding to a plate-like structure corresponding to the shape of the silicon flakes.

In this way, high purity silicon having a purity of 90 wt% or more, in detail, 95 wt% or more can be obtained from easily obtainable and cheap clay. With the above-mentioned production method, Do.

Specifically, the clay is not limited as long as it is a clay having a layered structure, but includes minerals selected from the group consisting of montmorillonite, mica, talc, and combinations thereof as clay minerals And, in particular, may be talc.

Thus, depending on the kind of the mineral contained in the clay, the kind of the metal oxide contained may be different. Therefore, the metal reducing agent for obtaining the silicon by reducing the silica contained in the clay is not limited to the silicon oxide contained in the clay The metal may be the same metal as the metal oxide excluding the metal oxides and more specifically may be a metal selected from the group consisting of Al, Mg, Ge, Fe, Ca, Ti, Cu, Zn, Ni, Zr, Cr, Ba, And more specifically Al or Mg. Such metal reducing agents may be in powder form, but are not limited thereto.

In the step i), the mixing ratio of the clay and the metal reducing agent may be such that the molar ratio of the oxygen of the silicon oxide contained in the clay to the metal reducing agent is 1: 0.5 to 1: 2.

If the amount of the metal reducing agent is too large, the metal reducing agent may be an impurity. When the amount of the metal reducing agent is too small, the remaining silica may not be reduced to silicon. It is not preferable.

The mixture of the clay and the metal reducing agent thus mixed is subjected to a heat treatment, and by the heat treatment, the silica contained in the clay is reduced to form silicon flakes, and the metal reducing agent is oxidized. An example of such a process is represented by the following formula:

_{(SiO 2) x (MgO)} y + 2xMg → xSi + (2x + y) MgO

(SiO ₂ ) x (Al ₂ O ₃ ) y + 4/3 x Al → xSi + (2 / 3x + y) MgO

The heat treatment of the above-mentioned step i) for the reduction reaction is performed at 500 to 800 degrees Celsius for 30 minutes to 6 hours, and more specifically, at 600 to 800 degrees Celsius for 1 to 3 hours .

When the temperature is too low or the time is short, the silica contained in the clay is not sufficiently reduced and silicon flakes are difficult to obtain. When the temperature is too high or the time is long, It is not preferable since the initial hole structure of the desired type such as rearrangement can not be obtained.

Further, the heat treatment may be performed in an atmosphere containing an inert gas, and more specifically, it may be performed in an atmosphere containing a gas selected from the group consisting of nitrogen gas, argon gas, neon gas, helium gas and combinations thereof And specifically can be performed under an argon gas atmosphere.

In this process, the oxidized metal reducing agent forms an oxide, which acts as an impurity, and can be removed by stirring with the acidic solution in the subsequent step ii) to obtain only the reduced silicon flake with high purity.

At this time, the step of stirring in the acidic solution of step ii) is carried out by stirring in a first acidic solution; And stirring the mixture in a second acidic solution can be carried out sequentially.

The stirring in the two acidic solutions is performed in order to remove both the metal oxide present in the mixture subjected to the reduction reaction by the heat treatment and the remaining silica which has not reacted.

The acidic solution used for the removal of the metal oxide and the silica is specifically the acid solution from the group consisting of hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, hydrofluoric acid, perchloric acid, chloric acid, chlorous acid, hypochlorous acid, iodic acid, It can be selected. The first and second acidic solutions may each independently be selected from the group consisting of hydrochloric, nitric, sulfuric, phosphoric, hydrofluoric, perchloric, chloric, chlorous, hypochlorous, iodic, . More specifically, the first acidic solution may be hydrochloric acid and the second acidic solution may be hydrofluoric acid. The hydrochloric acid dissolves the metal oxide, and the hydrofluoric acid dissolves the silica.

The process of stirring with the acidic solution as described above may be appropriately determined depending on the content of the remaining impurities, and specifically, it may be performed at 24 to 40 degrees Celsius for 5 minutes to 5 hours, , The stirring time with the first acidic solution can be specifically performed at 30 to 40 degrees Celsius for 2 to 5 hours and when the second acidic solution is hydrofluoric acid, the stirring time with the second acidic solution is For 5 to 30 minutes at room temperature.

The material having the impurities removed as described above can be obtained from the result of the stirring in the step (iii) above. The method of obtaining or separating the silicon flakes of the initial hollow structure is not particularly limited, but may be performed, for example, through filtering or centrifuging.

The method of obtaining the result contained in the solution by the centrifugal separator is as known in the art and the filtration may be a method through a vacuum filter in detail and a method for obtaining the resultant through a vacuum filter may be a vacuum filter After properly set up, the acid solution and other solvents can be separated from the silicon flakes by pouring the stirred solution into the vacuum filter vessel.

At this time, the method of obtaining by centrifugal separator has a problem that the volume of the solvent is at least 200 ml or more and it is difficult to complete separation when it is a neutral solution such as an acidic solution. More specifically, It is more preferable to synthesize a silicon flake having an initial hollow structure from a material.

In the meantime,

iv) supplying the carbon-containing gas to the obtained silicon flake and subjecting it to heat treatment.

By carrying out such a process, a carbon-coated silicon flake can be obtained.

At this time, the carbon-containing gas may be selected from acetylene gas, ethylene gas, propylene gas, methane gas, ethane gas, and combinations thereof, and more specifically, acetylene gas.

Further, the heat treatment of the above-mentioned process iv) for coating carbon through the carbon-containing gas may be performed for 1 minute to 30 minutes at 500 to 1,000 degrees, and for 1 minute to 10 minutes.

If it is carried out at too low a temperature outside of the above range, or if it is carried out for too short a time, a desired degree of carbon coating is not achieved and if it is carried out at too high a temperature or for a too long time, The crystal structure and the initial vacancy structure are affected and the structure can be modified in a form to form a complex with the silicon flake instead of the carbon-coated form, which is not preferable.

When carbon is coated on the silicon flakes using the carbon-containing gas in the completion of the manufacturing process, the carbon is not blocked by the pores of the silicon, so that the carbon has the connectivity and effectively forms the electron transfer path, It can be coated evenly on the surface of the silicon flakes. By forming a complex of silicon and a carbon compound by reacting the carbon compound in the middle of the production, the carbon compound forms a complex with silicon, Silicon carbide can be formed due to an excessive amount of heat generated in the metal thermal reduction reaction. However, such silicon carbide is electrochemically inactive, the structural maintenance of silicon flakes and the uniform carbon coating, And in terms of prevention of loss of active material The.

The present invention also provides a negative electrode including the negative electrode material and a secondary battery including such a negative electrode.

The secondary battery according to the present invention generally comprises an anode, a cathode, a separator, and a non-aqueous electrolyte containing a lithium salt. Therefore, other components constituting the lithium secondary battery in addition to the above-described negative electrode material according to the present invention will be described below.

The positive electrode is prepared by applying a mixture of a positive electrode active material, a conductive material, and a binder on a positive electrode current collector, and drying the mixture. Optionally, a filler may be further added to the mixture.

The cathode active material may be a layered compound such as lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), or a compound substituted with one or more transition metals; The formula Li _{1 + y} Mn _{2 - y} O ₄ (Where y is 0 to 0.33), lithium manganese oxides such as LiMnO ₃ , LiMn ₂ O ₃ and LiMnO ₂ ; Lithium copper oxide (Li ₂ CuO ₂ ); Vanadium oxides such as LiV ₃ O ₈ , LiFe ₃ O ₄ , V ₂ O ₅ and Cu ₂ V ₂ O ₇ ; Formula _{LiNi 1 - y M y O 2} ( where, the M = Co, Mn, Al, Cu, Fe, Mg, B or Ga, y = 0.01 ~ 0.3 Im) Ni site type lithium nickel oxide which is represented by; Formula _{LiMn 2 - y M y O 2} ( where, M = Co, Ni, Fe , Cr, and Zn, or Ta, y = 0.01 ~ 0.1 Im) or Li ₂ Mn ₃ MO ₈ (where, M = Fe, Co, Ni, Cu, or Zn); LiMn ₂ O _{4 in} which a part of Li in the formula is substituted with an alkaline earth metal ion; Disulfide compounds; Fe ₂ (MoO ₄ ) ₃ , and the like. However, the present invention is not limited to these.

The conductive material is usually added in an amount of 1 to 50% by weight based on the total weight of the mixture including the cathode active material. Such a conductive material is not particularly limited as long as it has electrical conductivity without causing chemical changes in the battery, and examples thereof include graphite such as graphene, graphite pellets, natural graphite and artificial graphite; Carbon black such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and summer black; Conductive fibers such as carbon fiber and metal fiber such as CNT; Metal powders such as carbon fluoride, aluminum, and nickel powder; Conductive whiskey such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives and the like can be used.

The binder is a component that assists in bonding between the active material and the conductive material and bonding to the current collector, and is usually added in an amount of 1 to 50 wt% based on the total weight of the mixture containing the cathode active material. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, polyacrylic acid (PAA), carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone , Ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butylene rubber, fluorine rubber, various copolymers and the like.

The filler is optionally used as a component for suppressing the expansion of the anode, and is not particularly limited as long as it is a fibrous material without causing a chemical change in the battery. Examples of the filler include olefin polymers such as polyethylene and polypropylene; Fibrous materials such as glass fibers and carbon fibers are used.

The cathode current collector generally has a thickness of 3 to 500 mu m. Such a positive electrode current collector is not particularly limited as long as it has high conductivity without causing chemical change in the battery, and may be formed of a material such as stainless steel, aluminum, nickel, titanium, sintered carbon, or a surface of aluminum or stainless steel Treated with carbon, nickel, titanium, silver or the like may be used. The current collector may have fine irregularities on the surface thereof to increase the adhesive force of the cathode active material, and various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric are possible.

The negative electrode is manufactured by binding an anode material, which is a mixture of an active material, a conductive material and a binder, to an anode current collector according to a conventional method known in the art, and plays a role of storing and releasing lithium ions like the anode .

In addition to the silicon flakes defined in the present invention, the negative electrode active material may include carbon black such as natural graphite, artificial graphite, channel black, acetylene black, ketjen black, furnace black, (SFG-6, SFG-15, etc.), highly oriented pyrolytic graphite, mesophase pitch based carbon fiber (MPCF), MCMB series (MCMB 2800, MCMB 2700, MCMB 2500, and the like), and can be used together with an ordered structure carbon material which is heat-treated at a temperature of 2000 ° C or higher and completely crystallized.

The negative electrode collector is generally made to have a thickness of 3 to 500 mu m. Such an anode current collector is not particularly limited as long as it has conductivity without causing chemical change in the battery, and may be formed of a material such as copper, stainless steel, aluminum, nickel, titanium, fired carbon, surface of copper or stainless steel A surface treated with carbon, nickel, titanium, silver or the like, an aluminum-cadmium alloy, or the like can be used. In addition, like the positive electrode collector, fine unevenness can be formed on the surface to enhance the bonding force of the negative electrode active material, and it can be used in various forms such as films, sheets, foils, nets, porous bodies, foams and nonwoven fabrics.

The negative electrode is prepared by coating a negative electrode current collector with a mixture of a negative electrode active material, a conductive material and a binder, and drying the mixture. Optionally, a filler may be further added to the mixture. The kind of the conductive material, the binder and the filler to be used at this time, and the formula (c) can be applied by referring to the contents described in the anode.

The separation membrane is interposed between the anode and the cathode, and an insulating thin film having high ion permeability and mechanical strength is used. The pore diameter of the separator is generally 0.01 to 10 mu m and the thickness is generally 5 to 300 mu m. Such separation membranes include, for example, olefinic polymers such as polypropylene, which are chemically resistant and hydrophobic; A sheet or nonwoven fabric made of glass fiber, polyethylene or the like is used. When a solid electrolyte such as a polymer is used as an electrolyte, the solid electrolyte may also serve as a separation membrane.

The lithium salt-containing non-aqueous electrolyte is composed of a non-aqueous electrolyte and a lithium salt. The non-aqueous electrolyte includes a non-aqueous organic solvent, an organic solid electrolyte, and an inorganic solid electrolyte.

Examples of the organic solid electrolyte include a polymer electrolyte such as a polyethylene derivative, a polyethylene oxide derivative, a polypropylene oxide derivative, a phosphate ester polymer, an agitation lysine, a polyester sulfide, a polyvinyl alcohol, a polyvinylidene fluoride, Polymers containing ionic dissociation groups, and the like can be used.

Examples of the inorganic solid electrolyte include Li ₃ N, LiI, Li ₅ NI ₂ , Li ₃ N-LiI-LiOH, LiSiO ₄ , LiSiO ₄ -LiI-LiOH, Li ₂ SiS ₃ , Li ₄ SiO ₄ , Nitrides, halides and sulfates of Li such as Li ₄ SiO ₄ -LiI-LiOH and Li ₃ PO ₄ -Li ₂ S-SiS ₂ can be used.

The lithium salt is a material that is readily soluble in the non-aqueous electrolyte, for example, LiCl, LiBr, LiI, LiClO 4, LiBF 4, LiB 10 Cl 10, LiPF 6, LiCF 3 SO 3, LiCF 3 CO 2, LiAsF _{6, LiSbF 6, LiAlCl 4,} CH 3 SO 3 Li, CF 3 SO 3 Li, (CF 3 SO 2) 2 NLi, chloroborane lithium, lower aliphatic carboxylic acid lithium, lithium tetraphenyl borate and imide have.

For the purpose of improving the charge / discharge characteristics and the flame retardancy, the electrolytic solution is preferably mixed with an organic solvent such as pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylenediamine, glyme, Benzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N, N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, . In some cases, a halogen-containing solvent such as carbon tetrachloride or ethylene trifluoride may be further added to impart nonflammability, or a carbon dioxide gas may be further added to improve high-temperature storage characteristics.

INDUSTRIAL APPLICABILITY As described above, the negative electrode material according to the present invention includes silicon flakes having an initial hollow structure synthesized from a cheap clay using a metal reducing agent, so that it is possible to reduce manufacturing cost and simplify the manufacturing process due to the synthesis of silicon flakes In the case of manufacturing a lithium secondary battery using the same, voids of various sizes mitigate the volume expansion of silicon, and even though it is micrometer-sized silicon, the initial hollow structure widens the contact area with the electrolyte, the movement distance of lithium ion is smaller than that of bulk silicon, and life time characteristics and rate characteristics are improved.

1 is a scanning electron microscope (SEM) photograph of the clay (Talc) used in Example 1. Fig.
2 is a scanning electron microscope (SEM) photograph of the silicon flake prepared in Example 1. Fig.
3 is a transmission electron microscope (TEM) photograph of the silicon flake prepared in Example 1. Fig.
4 is a high magnification transmission electron microscope (TEM) photograph of the silicon flake prepared in Example 1. Fig.
5 is an X-ray diffraction (XRD) graph of the silicon flake prepared in Example 1. Fig.
6 is a transmission electron microscope (TEM) photograph of the silicon flake prepared in Example 1, showing the formation of voids according to the reaction time.
7 is a scanning electron microscope (SEM) photograph of the carbon coated silicone flake prepared in Example 2. Fig.
8 is an x-ray diffraction (XRD) graph of the carbon coated silicone flake prepared in Example 2. Fig.
9 is a scanning electron microscope (SEM) photograph of the clay (Nanoclay) used in Comparative Example 1. Fig.
10 is a scanning electron microscope (SEM) photograph of the porous silicon produced in Comparative Example 1. Fig.
11 is a scanning electron microscope (SEM) photograph of a silicon flake prepared by adding a carbon compound in Comparative Example 2. Fig.
12 is an x-ray diffraction (XRD) graph of a silicon flake prepared by adding a carbon compound in Comparative Example 2. Fig.
13 is a scanning electron microscope (SEM) photograph of the carbon-coated porous bulk silicon produced in Comparative Example 3. Fig.
14 is a scanning electron microscope (SEM) photograph of a silicon flake having no initial hollow structure prepared in Comparative Example 4. Fig.
15 is an X-ray diffraction (XRD) graph of a silicon flake having no initial hollow structure prepared in Comparative Example 4. Fig.
16 is a scanning electron microscope (SEM) photograph of the silicon flake prepared in Comparative Example 5. Fig.
17 is a scanning electron microscope (SEM) photograph of the silicon flake produced in Comparative Example 6. Fig.
18 is an initial charge / discharge graph of a coin battery manufactured by using the silicon flakes of Example 1 and Example 2 as an active material in Experimental Example 4.
19 is an initial charge / discharge graph of a coin battery manufactured by using the bulk silicon of Comparative Example 1 as an active material in Experimental Example 4. FIG.
20 is an initial charging / discharging graph of a coin battery manufactured by using a silicon flake having a carbon compound of Comparative Example 2 added as an active material in Experimental Example 4. FIG.
21 is an initial charge / discharge graph of a coin battery manufactured by using the carbon-coated porous bulk silicon of Comparative Example 3 in Experimental Example 4 as an active material.
22 is an initial charge / discharge graph of a coin cell manufactured in Experimental Example 4 using a silicon flake having no initial hollow structure of Comparative Example 4 as an active material.
23 is a graph showing the charging / discharging lifetime characteristics of a coin battery manufactured by using the silicon flakes of Example 1 and Example 2 as an active material in Experimental Example 5. FIG.
24 is a graph showing the charging / discharging lifetime characteristics of a coin battery manufactured in Experimental Example 5 using carbon-coated silicon flakes of different thicknesses of Examples 3 and 4 as an active material.
25 is a graph showing the charging / discharging lifetime characteristics of a coin battery manufactured by using the bulk silicon of Comparative Example 1 as an active material in Experimental Example 5. FIG.
26 is a graph showing the charging / discharging lifetime characteristics of a coin battery manufactured by using the silicon flake with the carbon compound of Comparative Example 2 as an active material in Experimental Example 5. FIG.
27 is a graph showing the charging / discharging lifetime characteristics of a coin battery manufactured by using the carbon-coated porous bulk silicon of Experimental Example 5 and Comparative Example 3 as an active material.
28 is a graph showing the charging / discharging lifetime characteristics of a coin battery manufactured by using a silicon flake having no initial hollow structure of Comparative Example 4 in Experimental Example 5 as an active material.
FIG. 29 is a graph showing charge-discharge characteristics according to C-rate of a coin battery manufactured by using the silicon flakes of Examples 1 and 2 as an active material in Experimental Example 6. FIG.
30 is an SEM photograph of the diatomite used in Comparative Example 7. Fig.
31 is a SEM photograph of silicon flakes finally obtained in Comparative Example 7;
32 is an SEM photograph of the slag used in Comparative Example 8;
33 is a SEM photograph of the silicon flakes finally obtained in Comparative Example 8. Fig.
34 is an initial charge / discharge graph of a coin cell manufactured in Experimental Example 4 using the silicon materials of Examples 1, 2, 7, and 8 as an active material, respectively.
35 is a graph showing the charging / discharging lifetime characteristics of a coin battery manufactured by using the silicon material of Examples 1, 2, 7 and 8 in Example 5 as an active material.
36 is a graph showing charge-discharge characteristics according to C-rate of a coin battery manufactured by using the silicon material of Example 1, Example 2, Comparative Example 7, and Comparative Example 8 as an active material in Experimental Example 6. FIG.
37 is a TEM photograph of a silicon flake subjected to a heat treatment at 650 ° C. for 6 hours.
38 is a schematic diagram of a silicon flake having an initial hyperporous structure according to an embodiment of the present invention.

Hereinafter, the present invention will be described in further detail with reference to the following examples. However, the following examples are intended to illustrate the present invention and the scope of the present invention is not limited thereto

&Lt; Example 1 >

1 g of Talc was uniformly mixed with 0.7 g of magnesium and a mortar. The homogeneously mixed mixture was placed in a reaction vessel, and a reduction reaction was performed by heating in an argon atmosphere at 650 ° C. for 3 hours. After the reaction, the silicone flakes were mixed in a 0.5M aqueous 200mL hydrochloric acid solution at 35 ° C for 3 hours, and magnesium oxide and other foreign substances were removed. The removal of the remaining silica after the reaction was carried out by mixing 0.1 to 5% of hydrofluoric acid with silicon flakes for 5 to 30 minutes. Silicon flakes of the initial hollow structure were finally synthesized through a vacuum filter.

&Lt; Example 2 >

The silicon flakes synthesized in Example 1 were subjected to acetylene gas blowing for 3 minutes in a 900 degree argon atmosphere, and the reaction was carried out. After cooling naturally to room temperature, a carbon-coated silicon plate was finally synthesized to a thickness of 9 nm.

&Lt; Example 3 >

Silicon flakes were synthesized in the same manner as in Example 2, except that the thickness of the carbon layer was changed to 5 nm.

<Example 4>

A silicon flake was synthesized in the same manner as in Example 2, except that the thickness of the carbon coated was 15 nm.

&Lt; Comparative Example 1 &

All processes are the same except for the kind of clay used in the synthesis example of the silicone flake. Namely, the clay used in Comparative Example 1 is Nanoclay.

&Lt; Comparative Example 2 &

A silicone composite including the graphene oxide was obtained in the same manner as in Example 1, except that 0.05 g of carbon compound was added and reacted with 1 g of the clay in Example 1.

&Lt; Comparative Example 3 &

50 g of bulk silicon is added to 100 mL of a mixed solution of 40 mM CuSO ₄ and 5 M HF, followed by stirring at 50 ° C. for 12 hours. After the reaction, the porous silicon including the large pore was filtered through a filter, and the remaining Cu metal was removed by stirring in 50 mL of nitric acid solution at 50 ° C for 3 hours. The porous silicon was subjected to acetylene gas blowing in a 900 degree argon atmosphere for 28 minutes, and the reaction was carried out. After cooling to room temperature naturally, porous silicon coated with 15 wt% of carbon was finally synthesized.

&Lt; Comparative Example 4 &

Silicone flakes were synthesized in the same manner as in Example 1, except that the kind of clay used was Illite.

&Lt; Comparative Example 5 &

In Example 1, silicon flakes were synthesized in the same manner except that the reduction reaction temperature was set at 400 deg.

&Lt; Comparative Example 6 >

In Example 1, a silicon flake was synthesized in the same manner except that the reduction reaction time was changed to 10 minutes.

&Lt; Comparative Example 7 &

Silicone flakes were synthesized in the same manner as in Example 1, except that diatomite was used instead of clay (Talc).

&Lt; Comparative Example 8 >

Silicone flakes were synthesized in the same manner as in Example 1, except that slag was used instead of clay (Talc). The slag used in this case is also called an iron slag and its composition is CaO (43.3 wt%), SiO ₂ (34.5 wt%), Al ₂ O ₃ (13.3 wt%), MgO (3.6 wt% ₂ (1.7 wt%), and Fe ₂ O ₃ (1.1 wt%).

<Experimental Example 1>

Experimental Example 1-1

For appearance evaluation, SEM photographs and / or TEM photographs of the clay used in Examples 1 and 2 and Comparative Examples 1 to 6 and silicon flakes or bulk silicon produced using the same, and FIGS. 1 to 4, 7, 9 to 11 and 13, 14, 16, and 17, respectively.

Specifically, FIG. 1 is an SEM photograph of the clay (Talc) used in Example 1, and FIG. 2 is an SEM photograph of the silicon flakes finally obtained in Example 1. FIG.

Referring to FIG. 1, a layered structure of the raw material, Talc, can be identified, which includes 2 to 4 stacked flakes through the covalent bonds of silica and metal oxide, When the flakes are formed into a single unit structure, it can be confirmed that the flakes have a thickness of 50 to 200 nm.

Referring to FIG. 2, it can be seen that the silicon flake synthesized in Example 1 has an initial hollow structure.

In order to more specifically understand the structure of the silicon flake finally obtained in Example 1, a TEM photograph was taken and shown in FIG.

Referring to FIG. 3, it can be seen that a large pore size of 100-150 nm is uniformly formed on the surface of the silicon flakes, and it can be confirmed that the silicon flakes are piled up in two to four layers.

The internal view of FIG. 4 is the high magnification image of FIG. Referring to FIG. 4, it can be seen that mesopore and micropores are formed on the surface of the silicon flake.

3 and 4, it can be seen that the silicon flake according to Example 1 has an initial hollow structure.

7 is an SEM photograph of the carbon coated silicon flake made in Example 2, and the internal view of FIG. 7 is the high magnification image of FIG. 7. FIG.

Referring to FIG. 7, it can be seen that even after the carbon layer is coated, the silicon flakes maintain the initial hollow structure.

9 is an SEM photograph of the clay (Nanoclay) used in Comparative Example 1, and Fig. 10 is a SEM photograph of the bulk silicon finally obtained in Comparative Example 1. Fig.

Referring to FIG. 9, it can be seen that the layered structure of the raw material, Nanoclay, includes a nanosheet laminated through covalent bonding of silica and metal oxide, and a laminated nanosheet , It can be confirmed that it has a thickness of about 10 to 50 nm.

On the other hand, referring to FIG. 10, it can be seen that the silicon synthesized in Comparative Example 1 can not confirm the existing layer structure and shows a structure of three-dimensional bulk silicon mainly having large pores of 100 to 300 nm.

In the case of nanoclays, since the internal metal oxide (ie, aluminum oxide) can not act as a negative catalyst (heat catalyst), the excess heat generated in the reduction reaction is transferred directly to the structure, You can see how nano-clays are assembled. And 100 to 300 nm large pores formed by removing MgO formed as a result of reduction are all, and thus do not have an initial hollow structure. For this reason, it is impossible to maintain a conventional layered structure or a layered structure such as a silicon flake.

11 is an SEM photograph of a silicon flake to which the carbon compound prepared in Comparative Example 2 is added, and an internal view of FIG. 11 is a high magnification image of FIG.

11, it was confirmed that the flake structure was maintained at a constant level in the case of silicon flakes synthesized by adding a carbon compound. However, due to the fact that the carbon compound interferes with the reduction reaction during the reduction reaction, It can be confirmed that a non-uniform structure is formed.

13 is a SEM photograph of the carbon-coated porous bulk silicon produced in Comparative Example 3. Fig.

Referring to FIG. 13, the porous structure composed only of the large pores is formed in the three-dimensional bulk silicon, and the initial porous structure can not be confirmed.

 Further, in order to more specifically grasp the structure of the silicon flake finally obtained in Comparative Example 4, a SEM photograph was taken and shown in FIG.

Referring to FIG. 14, the silicon produced from the raw material illite shows the structure of flakes, but it can be confirmed that there is no initial hollow structure on the surface.

15 is an X-ray diffraction (XRD) graph of a silicon flake having no initial hollow structure prepared in Comparative Example 4. Fig.

16 is an SEM photograph of the silicon flake obtained in Comparative Example 5, and the internal view of FIG. 16 is the high magnification image of FIG.

Referring to FIG. 16, it can be seen that the silicon flake synthesized at a temperature of 400 ° C. has a flake structure of the used clay, but the structure of the pore is irregular and the initial hollow structure can not be realized.

The normal magnesium reduction reaction occurs when magnesium reacts with silica while the magnesium is dissolved near the melting point of magnesium. At 400 ° C, magnesium does not completely participate in the reaction, resulting in complete reduction of the silicon flake, It was also not formed.

17 is a SEM photograph of the silicon flake obtained in Comparative Example 6. Fig.

17 is the high magnification image of Fig. Referring to FIG. 17, it can be seen that no large pore was formed on the surface of the silicon flake under the reaction condition of 650 ° C. for 10 minutes, and a layer composed of mesopores and micropores covers the surface. When the reaction time is 10 minutes, the reaction is not sufficiently carried out, indicating that the silicon flakes do not completely complete the initial tool set.

16 and 17, the validity of the synthesis conditions including the reaction temperature and the reaction time applied in Example 1 can be confirmed.

Experimental Example 1-2

For appearance evaluation, SEM photographs of the diatomaceous earth and slag used in Comparative Examples 7 and 8 and the silicon flakes made using it are shown in FIGS. 30-33.

30 is an SEM photograph of the diatomite used in Comparative Example 7, and FIG. 31 is an SEM photograph of the silicon flakes finally obtained in Comparative Example 7. FIG.

32 is an SEM photograph of the slag used in Comparative Example 8, and FIG. 33 is an SEM photograph of the silicon flakes finally obtained in Comparative Example 8. FIG.

In comparison with the case where the porous silicon of the two-dimensional structure was synthesized, the porous silicon of the three-dimensional structure in Comparative Example 7 and the porous silicon of the comparative example 8 were obtained in comparison with the silicon flakes produced using Talc as the clay, Mesoporous silicon particles were synthesized, and no initial hollow structure was formed.

<Experimental Example 2>

TEM photographs of the silicon flakes finally obtained in Example 1 are shown in FIG. 6 in order to more specifically understand the process of forming void structure according to the reaction time of the silicon flakes.

Referring to FIG. 6, when the reaction time is 10 minutes, the pore structure of the silicon flake can hardly be observed, and it can be confirmed that all the surfaces are composed of the medium phase. It can be seen that the thickness was also larger than the level of the clay. Further, it can be confirmed that the crystallinity of silicon is inferior.

When the reaction time is 30 minutes, the structure of the large pore structure has begun to be realized, and it can be seen that due to the heat of reaction, a single layer of silicon flakes peeled off from the laminated structure of the clay is formed.

Further, it can be confirmed that 50 to 70% of the surface of the silicon flake is composed of a medium-phase core, and the crystallinity is increased.

When the reaction time is one hour, the size of the large pores becomes more uniform, and it can be seen that the peeled silicon flakes begin to be stacked in two or three layers, considering that the large pores are overlapped.

Also, it can be seen that 10 to 30% of the surface of the silicon flake is composed of a medium-phase core, and the crystallinity is increased.

When the reaction time was 3 hours, the size of the large pore was somewhat smaller, and it can be confirmed that the pore was stacked in 3 to 4 layers.

Further, the mesoporous structure of the surface of the silicon flake disappears, and a frame of a dense structure can be confirmed.

As a result, the TEM photograph of FIG. 6 is analyzed in a comprehensive manner. In the initial stage of the reaction by the metal reducing agent, mesoporous voids are formed on the surface excessively and the reaction progresses to the inside of the clay as time goes by, And when the reaction time exceeds 30 minutes, it is seen that it is laminated again, and the size of the large pore decreases also. Therefore, in order to obtain the silicone flake according to the present invention, it is necessary to have a reaction time of at least 30 minutes, more specifically, a reaction time of 1 hour to 3 hours.

37 is a TEM photograph of a silicon flake subjected to a heat treatment at 650 ° C. for 6 hours. Referring to FIG. 37, it can be seen that as the heat treatment time is increased, the overall particle size increases. This is typically seen as a phenomenon of agglomeration when a long reaction is carried out at high temperatures. One more unusual point is that the size of the large pore becomes finer and the boundary is not clearly visible . The reason for this is that many layers of silicon flakes appear together.

<Experimental Example 3>

In order to grasp the structure of the silicon flakes finally obtained in Examples 1 and 2 and Comparative Examples 2 and 4, an XRD graph was prepared and shown in FIGS. 5, 8, 12 and 15.

The XRD instrument (D8 Advance, Bruker) used for this measurement was measured at 3 kW X-ray generation power, 20 kV measurement voltage, 50 mA measurement current, and 10 ° to 90 ° measurement range.

Referring to Figures 5, 8 and 12, it can be seen that pure silicon was synthesized without any other impurities.

Referring to FIG. 8, although a thin carbon layer is coated, it is insufficient to be observed through XRD analysis. Referring to FIG. 12, silicon and oxidized graphene are present together.

<Experimental Example 4>

Experimental Example 4-1

Various silicones prepared in Example 1 and Comparative Examples 1 to 4 were used as an anode active material, PAA (polyacrylic acid) / CMC as a binder, and carbon black as a conductive material. Negative electrode active material: binder: The conductive material was mixed well with water to a weight ratio of 8: 1: 1, applied to a Cu foil having a thickness of 18 탆, and dried at 150 캜 to prepare a negative electrode. Lithium foil was used as the anode, and an electrolyte solution containing 1 M of LiPF ₆ and 10 weight% of FEC (fluoroethylene carbonate) in a solvent of EC (ethylene carbonate): DEC (diethyl carbonate) = 3: A half-coin cell was prepared.

The discharge capacity and charge / discharge efficiency results of the thus fabricated half-coin cell were measured at an applied current of 0.25 C at 25 ° C and a voltage range of 0.01 to 1.2 V, and the discharge capacity and charge / discharge efficiency results are shown in FIGS. 18 to 22.

Referring to FIG. 18, the half-coin cell made of silicon flakes and carbon coated silicon flakes exhibited charge / discharge ratio capacities of 2209/2383 and 2984/3216, respectively, and initial charging and discharging of 92.67% and 92.77% Efficiency.

On the other hand, referring to FIG. 19, a half-coin cell made of bulk silicon manufactured from Nanoclay exhibits a charge / discharge ratio capacity of 1772/2497 and an initial charge / discharge efficiency of 70.96%.

Referring to FIG. 20, a half-coin cell made of a silicon flake with a carbon compound added exhibits a charge / discharge ratio capacity of 2027/2475 and an initial charge / discharge efficiency of 81.9%.

Referring to FIG. 21, a half-coin cell made of carbon-coated porous silicon manufactured through a metal-assisted chemical etching method exhibits a charge / discharge ratio capacity of 2565/2886 and an initial charge / discharge efficiency of 88.88%.

Referring to FIG. 22, a half-coin cell made of a silicon flake having no initial hollow structure exhibits a charge / discharge ratio of 1243/1381 and exhibits an initial charge / discharge efficiency of 90.05%.

Experimental Example 4-2

Various silicones prepared in Examples 1, 2, 7 and 8 were used as an anode active material, PAA (polyacrylic acid) / CMC as a binder, and carbon black as a conductive material. Negative electrode active material: binder: The conductive material was mixed well with water to a weight ratio of 8: 1: 1, applied to a Cu foil having a thickness of 18 탆, and dried at 150 캜 to prepare a negative electrode. Lithium foil was used as the anode, and an electrolyte solution containing 1 M of LiPF ₆ and 10 weight% of FEC (fluoroethylene carbonate) in a solvent of EC (ethylene carbonate): DEC (diethyl carbonate) = 3: A half-coin cell was prepared.

The discharge capacity and the charging / discharging efficiency of the thus fabricated half-coin cell were measured at an applied current of 0.25 C at 25 캜 and a charging / discharging capacity of 0.01 to 1.2 V in a voltage range.

34, a half-coin cell made of silicon flakes (Example 1) and carbon-coated silicon flakes (Example 2) exhibits charge / discharge ratio capacities of 2209/2383 and 2984/3216, respectively, The initial charging and discharging efficiencies were 92.67% and 92.77%, respectively.

On the other hand, in the case of silicon synthesized from diatomaceous earth and slag (Comparative Example 7 and Comparative Example 8), the respective charge / discharge capacities of 2742/3483 and 2320/2674 are shown, and the initial charge and discharge efficiencies of 78.77% and 86.76 are shown .

In conclusion, the use of the silicon flakes according to the present invention as an active material shows a significantly higher initial charge-discharge efficiency as compared with the case of using silicon flakes without bulk silicon and an initial hollow structure, and further, The initial charge / discharge efficiency is higher than that of silicon flake and carbon-coated porous silicon.

<Experimental Example 5>

Experimental Example 5-1

The carbon coated silicon prepared in Examples 3 and 4 was used as an anode active material, and PAA / CMC as a binder and carbon black as a conductive material were used. Negative electrode active material: binder: The conductive material was mixed well with water to a weight ratio of 8: 1: 1, applied to a Cu foil having a thickness of 18 탆, and dried at 150 캜 to prepare a negative electrode. Lithium foil was used as the anode, and an electrolyte solution containing 1M LiPF ₆ and 10 weight ratio FEC in a solvent of EC: DEC = 3: 7 was used to prepare a half coin cell.

The lifetime characteristics were evaluated by charging and discharging the half-coin cells manufactured above and the half coin cells manufactured in Experimental Example 4 at a current of 0.2 C (1 C = 3 A / g) 100 times, 23 to Fig. 28.

Referring to FIG. 23, half-coin cells prepared using silicon flakes (Example 1) and carbon-coated silicon flakes (Example 2) as active materials were subjected to a 100 charge / discharge cycle at a rate of 0.2 C, % And 94.6%, respectively.

Referring to FIG. 24, lifespan characteristics of the half-coin cells prepared by using the silicon flakes of Examples 3 and 4 as an active material after 100 cycles of 0.2 C rate charge / discharge cycle were shown. And showed sufficiently good life characteristics as compared with other comparative examples.

Referring to FIG. 25, it can be confirmed that the half-cell manufactured using bulk silicon of Comparative Example 1 as an active material has a lifetime after 100 charge / discharge cycles of 0.2 C rate.

Referring to FIG. 26, not only the half-coin cell made of silicon flakes with a carbon compound added shows a sharp decrease even at a charge / discharge cycle of 0.2C, but after 18 cycles of charging and discharging at a rate of 0.5C, Cycle life only.

Referring to FIG. 27, it can be seen that the half-coin cell made of carbon-coated porous silicon also fulfills its life after 100 charge / discharge cycles at 0.2 C rate.

Referring to FIG. 28, a half-coin cell manufactured from a silicon flake having no initial hollow structure exhibits a cycle life of 71.74% after 90 cycles of 0.2C rate charge / discharge.

Experimental Example 5-2

Various silicones prepared in Examples 1, 2, 7 and 8 were used as an anode active material, and PAA / CMC as a binder and carbon black as a conductive material were used. Negative electrode active material: binder: The conductive material was mixed well with water to a weight ratio of 8: 1: 1, applied to a Cu foil having a thickness of 18 탆, and dried at 150 캜 to prepare a negative electrode. Lithium foil was used as the anode, and an electrolyte solution containing 1M LiPF ₆ and 10 weight ratio FEC in a solvent of EC: DEC = 3: 7 was used to prepare a half coin cell.

The half-cells thus prepared were charged and discharged 50 times at a current of 0.2 C (1 C = 3 A / g) to evaluate the lifetime characteristics. The results are shown in FIG.

35, half-coin cells made of silicon flakes (Example 1) and carbon-coated silicon flakes (Example 2) were subjected to 50% charge and discharge cycles at 0.2 C rate, and then 100% and 95.97% Lt; / RTI &gt; On the other hand, in the case of silicon synthesized from diatomaceous earth and ferro-Si (Comparative Example 7 and Comparative Example 9), the life characteristics were 56.47% and 71.36%, respectively.

As a result, when using the silicon flakes according to the present invention as an active material, the silicon flakes exhibit excellent cycle life as compared with the case of using the silicon flakes without bulk silicon and the initial hollow structure, and further, In the case of using a carbon-coated silicon flake, the lifetime characteristics are significantly improved.

<Experimental Example 6>

According to Experimental Example 4, half-coin cells using the silicon flakes prepared in Examples 1 and 2 as anode active materials were charged and discharged at currents of 0.2C, 0.5C, 1C, 2C, 5C and 10C , And the results are shown in Fig.

Referring to Figure 29, half-coin cells made from silicon flakes (Example 1) and carbon coated silicone flakes (Example 2) exhibit a specific capacity of about 25 and 585 at 10 C rate.

Further, according to Experimental Example 4, half-coin cells using the silicon flakes prepared in Example 1, Example 2, Comparative Example 7, and Comparative Example 8 were used as negative electrode active materials and 0.2C, 0.5C, 1C, 2C, and 5C. The results are shown in FIG.

Referring to FIG. 36, when the silicon flakes of Example 1 and the carbon-coated silicon flakes of Example 2 were used as negative active materials, the specific capacities of 134 and 958 at 5 C, respectively, and the diatomite of Comparative Example 7, And Ferro-Si of Comparative Example 8, respectively, the specific capacities of 28 and 87 were shown. (Non-capacity unit mAhg- ¹ )

As a result, when silicon flakes according to the present invention are used as an active material, they exhibit excellent performance in terms of rate characteristics. However, the use of carbon-coated silicon flakes is remarkably superior in terms of rate characteristics.

The electrochemical analysis showed that the silicon flakes and the carbon-coated silicon flakes according to an embodiment of the present invention are superior to other silicon materials synthesized through Mg reduction in terms of initial efficiency, lifetime characteristics, and rate characteristics Could know.

The reason for this performance improvement can be explained as follows.

First, the silicon flake according to one embodiment of the present invention can greatly improve the electrolyte impregnation characteristic through the initial hollow structure. Most of the porous silicon structures have pores only on the surface thereof, whereas the silicon flakes according to an embodiment of the present invention have large macropores formed on the entire structure, so that the electrolyte is uniformly contacted with the electrode material from the initial cycle It can help improve the diffusion of lithium ions.

Second, the silicon flakes according to an embodiment of the present invention may be advantageous in terms of accommodating volume expansion because they are composed of various kinds of pores such as hollow pores and hollow pores and micropores. The silicon flakes according to an embodiment of the present invention are applied to a silicon anode active material having a two-dimensional porous structure, as compared with those having a three-dimensional porous structure. It can be completely differentiated.

In addition, the silicon flake according to an embodiment of the present invention can exhibit an excellent reversible capacity at a high C rate in spite of a large particle size, and it is possible to improve the diffusion property of lithium ion And is advantageous in terms of accommodating volume expansion. The reason why a material having a two-dimensional structure than a three-dimensional structure is advantageous in terms of volume expansion is that the material of the two-dimensional structure can maintain the structure of the structure better, and the material of the three- This is because the structure changes into a two-dimensional structure after several cycles. In the case of a two-dimensional structure, it has an expansion in the plane direction and a vertical direction, and even considering the same volume expansion, the actual expansion ratio in the electrode is much smaller, which is superior to the three-dimensional structure material expanding in all directions.

38 is a schematic diagram of a silicon flake having an initial hyperporous structure according to an embodiment of the present invention. Referring to FIG. 38, the most rounded portion is a large air gap, and pores located on the surface correspond to mesopores and micropores. That is, the hollow pores and the microvoids are formed on the frame surface of the silicon flakes, and the pores correspond to the holes inside the silicon flake frame, i.e., the frame itself.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not to be limited to the details thereof and that various changes and modifications will be apparent to those skilled in the art. And various modifications and variations are possible within the scope of the appended claims.

Claims (19)

An anode material comprising a silicone flake represented by the following formula (1) and having an initial hyperporous structure as an active material:
xSi (1-x) A (1)
In this formula,
0.5? X? 1.0;
A is an _{impurity, Al 2 O 3, MgO,} SiO 2, GeO 2, Fe 2 O 3, CaO, TiO 2, Na 2 OK 2 O, CuO, ZnO, NiO, Zr 2 O 3, Cr 2 O 3 And BaO. The method according to claim 1,
The silicon flake has an initial hollow structure comprising a large void having a pore size in the range of greater than 50 nm to 500 nm, a hollow electrode having a pore size greater than 2 nm to 50 nm, and micropores having a pore size of 0.5 nm to 2 nm And the anode material. The method according to claim 1,
Wherein the silicon flake has an average pore diameter of 100 nm to 150 nm. The method according to claim 1,
Wherein the silicon flakes have a porosity of 10% to 50% based on the total volume. The method according to claim 1,
Wherein the silicon flake has a thickness of 20 to 100 nm. The method according to claim 1,
Wherein the silicon flake has a size of 200 nm to 50 占 퐉. The method according to claim 1,
Wherein the silicon flakes have a BET surface area of 70 m ² / g to 250 m ² / g. The method according to claim 1,
RTI ID = 0.0 &gt; 1, &lt; / RTI &gt; wherein the silicon flake further comprises a carbon coating. 9. The method of claim 8,
Wherein the carbon coating has a thickness of 1 to 100 nm. A method of making a silicone flake according to claim 1,
i) heat treating the mixture of clay and metal reducing agent at 500 to 800 degrees Celsius for 30 minutes to 6 hours;
ii) stirring the heat-treated mixture in an acidic solution; And
and iii) obtaining a silicon flake having an initial hollow structure from the result of the stirring. 11. The method of claim 10,
The method of producing a silicon flake comprises:
and iv) supplying a carbon-containing gas to the silicon flake to heat-treat the silicon flake. 11. The method of claim 10,
Wherein said clay comprises minerals selected from the group consisting of montmorillonite, mica, talc, and combinations thereof as clay minerals. 11. The method of claim 10,
Wherein the metal reducing agent is the same metal as the metal oxide excluding the silicon oxide contained in the clay. 11. The method of claim 10,
Wherein the mixing ratio of the clay and the metal reducing agent in the step i) is controlled so that the molar ratio of the oxygen of the silicon oxide contained in the clay to the metal reducing agent is 1: 0.5 to 1: 2. 11. The method of claim 10,
The step of stirring in an acidic solution of the step ii) is carried out by stirring in a first acidic solution; And stirring the mixture in a second acidic solution in sequence. 11. The method of claim 10,
The first acidic solution and the second acidic solution of step ii) are each independently selected from the group consisting of hydrochloric, nitric, sulfuric, phosphoric, hydrofluoric, perchloric, chloric, chlorous, hypochlorous, &Lt; / RTI &gt; is selected. 16. The method of claim 15,
Wherein the first acidic solution is hydrochloric acid and the second acidic solution is hydrofluoric acid. 12. The method of claim 11,
Wherein the carbon-containing gas is selected from acetylene gas, ethylene gas, propylene gas, methane gas, ethane gas, and combinations thereof. 12. The method of claim 11,
Wherein the heat treatment in step iv) is performed at 500 to 1000 degrees for 1 to 30 minutes.

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